1. Field of the Invention
This invention relates to flame resistant articles. More particularly, this invention relates to ballistic or impact resistant articles having improved flame resistance.
2. Prior Art
Ballistic articles such as bulletproof vests, helments, structural members of helicopters and other military equipment, vehicle panels, briefcases, raincoats and umbrellas containing high strength fibers are known. Fibers conventionally used include aramide fibers such as poly(phenylenediamine terephthalamide), graphite fibers, nylon fibers, ceramic fibers, glass fibers and the like. For many applications, such as vests or parts of vests, the fibers are used in a woven or knitted fabirc. For many of the applications, the fibers anre encapsulted or embedded in a matrix material.
In "The Application of High Modulus Fibers to Ballistic Protection", R. C. Laible et al., J. Macromol. Sci.-Chem., A7(1), pp. 295-322, 1973, it is indicated ono p. 298 that a fourth requirement is that the textile material have a high degree of heat resistance. In an NTIS publication, AD-A018 958 "New Materials in Construction for Improved Helmets", A. L. Alesi et al., a multilayer highly oriented polypropylene film material (without matrix), referred to as "XP", was evaluated against an aramid fiber (with a phenolic/polyvinyl butyral resin matrix. The aramid system was judged to have the most promising combination of superior performance and a minimum of problems for combat helmet development.
U.S. Pat. Nos. 4,403,012 and 4,457,985 disclose ballistic resistant composite articles comprised of networks of high molecular wight polyethylene or polypropylene fibers, and matrices composed of olefin polymers and copolymers, unsaturated polyester resins, epoxy resings, and other resins curable below the melting point of the fiber.
A. L. Lastnik, et al., "The Effect of Resin Concentration and Laminating Pressures of KEVLAR Fabric Bonded with Modified Phenolic Resin", Tech. Report NATICK/TR-84/030, Jun. 8, 1984; disclose that an interestitial resin, which encapsulates and bonds the fibers of a fabric, reduces the ballistic resistance of the result composite article.
U.S. Pat. Nos. 4,623,574 and 4,748,064 disclose a simple composite structure comprising high strength fibers embedded in an elasomeric matrix. The simple composite structure exhibits outstanding ballistic protection as compared to simple composites utilizng rigid matrices, the result of which are disclosed in the patent. Particularly effective are simple composites utilizing rigid matrices, the result of which are disclosed in the patents. Particularly effective are simple composites employing ultra-high molecular weight polyethylene and polypropylene such as disclosed in U.S. Pat. No. 4,413,110.
U.S. Pat. Nos. 4,737,402 and 4,613,535 disclose complex rigid composite articles having improved impact resistance which comprise a network of high strength fibers such as the ultra-high molecular weight polyethylene and polypropylene disclosed in U.S. Pat. No. 4,413,110 embedded in an elasomeric material and at least one additional rigid layer on a major surfact of the fibers in the matrix. It is disclosed that the composites have improved resistance to environmental hazards, improved impact resistance and are unexpectedly effective as ballistic resistant articles such as armor.
U.S. Pat. No. 4,650,710 discloses a ballistic resistant fabric article which comprises at least one network of fibers selected from the group consisting of extended chain polyethylene, polypropylene, polyvinyl alcohol and polyacrylonitrile fibers coated with a low modulus elastomeric material.
U.S. Pat. No. 4,681,792 discloses a flexible article of manufacture comprising a plurality of first flexible layers arranged in a first portion of the article, each of said first layers consisting essentially of fibers having a tensile modulus of at least about 300 g/denier and a tenacity of at least about 15 g denier and a plurality of second flexible layers arranged in a second portion of said article, each of said second flexible layers comprising fibers, the resistance to displacement of fibers in each of said second flexible layers being greater than the resistance to displacement in each of said first flexible layers.
U.S. Pat. No. 4,543,286 discloses a ballistic-resistant fabric article of manufacture comprising at least one network of extended chain polyolefin fibers selected from the group consisting of extended chain polyethylene and extended chain polypropylene fibers in a matrix, the fibers are coated with at least 0.01 to 200% of a polymer having ethylene or propylene crystallinity.
U.S. Pat. No. 4,916,000 discloses a composite of at least one layer which comprises a network of filaments in a matrix, wherein that ratio of thickness of the layer to filament diameter is less than about 12.8.
U.S. Pat. No. 4,737,401 discloses composites of polyethylene, polyperopylene, polyvinyl alcohol and polyacrylonitrile of low denier (under 500) and low tensile modulus-(200 grams/denier).
U.S. Pat. No. 4,868,040 discloses the use of Al(OH).sub.3 as a flame retardant in vinyl ester resin matrixes to reduce smoke production and to enhance flame retardancy of the armor composite.
Fire retardant compositions are known. For example, A. H. Landrocki, "Handbood of Plastic Flammabiltiy Fuel and combustion Toxicology," (Noyes Publication, 1983) disclosures the basic front line of fire/flame retardants. Basically, flame retardants for plastics function under heat to yield products that would be more difficult to ignite than the virgin plastics, or that do not propagate flame as readily. They function in one or more ways. For example, they absorb heat, thereby making sustained burning more difficult, and they form nonflammable char or coating that insulates the substrate from the heat, excludes oxygen, and slows the rate of diffusion of volatile, flammable pyrolysis fragments from the substrate. Flame retardants for plastics may also function by enhancing the decompositon of the substrate, thereby accelerating its melting al lower temperatures so that it drips or flows away from the flame front and by evolving products that stop or slow flame propagation. Still other flame retardants for plastics may function by forming free radicals that convert a polymer to less combustible products and by excluding oxygen from possible burning sites by coating resin particles.
Fire-retardant chemicals available commercially for plastics can be divided into two general classes, unreactive additives and reactive monomers or crosslinking agents. The unreactive additives are generally added to the polymer during processing, but do not react chemically with the other constituents of the composition. The reactive types, on the other hand, chemically react with the polymer structure at some processing stage.
The ideal fire retardant additives should be inexpensive, colorless, easily incorporated into the polymer composition, compatible, stable to heat and light, efficient in its fire-retardant properties, nonmigrating, and have no adverse effects on the physical properties of the polymer. The toxicology of the additive is also of concern. Unfortunately, most presently available additives seldom meet all these requirements.
Additive flame-retardant systems are generally composed of both organic and inorganic materials acting to provide an optimum balance of flame retardance, physical properties and cost. Additive retardants are generally incorporated by compounding and are useful in a variety of polymer systems. These materials are generally used for thermoplastic resins, although there are exceptions. With few exceptions, additive resins are used to fire retard flexible polyurethane foams. Halogenated organic compounds, such as PVC, or decabromodiphenyl oxide (DBDPO) in combination with antimony oxide typifies this type of system. DBDPO has long been the standard of comparison in many rigid plastics. Other compounds of this type include polychlororene, chlorinated polyethylene, and chlorosulfonated polyethylene, chlorinated parraffins, tris(dichloropropyl)phosphate, methyl pentachlorostearate, and various chlorinated phosphates for polyurethane foams and topical fabric treatment; cycloaliphatic chlorine-containing flame retardants (with higher thermal stability) for thermoplastics like polypropylene and nylon; and chlorendic anhydride, which is used as an intermediate in making flame retardant polyesters and epoxy resins.
Reactive flame retardant systems contain functional groups allowing them to be incorporated directly into the polymer structure through chemical reactions. The main advantage of this type of fire retardant is the permanence of the fire retardancy imparted. In most cases, chemically reacting the fire retardant into the polymer essentially eliminates long-term migration of the fire retardant.
Reactive flame retardants are primarily used in unsaturated polyesters, epoxy resins and polyurethane foams. Two of the most popular reactive flame retardants are tetrabrombisphenol A and dibromomononeopentyl and tetrabromophthalic glycol. Other reactive flame retardants include chlorendic acid and chlorendic anhydride, tetrabromophthalic and tetrachlorophthalic anhydride, and diallyl chlorendate. Other reactive flame retardants vary significantly in functionality and can be useful in many polymer reactions and applications. Reactive polyols which contain halogen groups, phosphorus, or both are used for flame-retardant urethane foam applications. These materials can be used alone, or with other flame retardants.
It is known that certain types of resins exhibit fire retardant properties. For example, thermosetting polymers differ from thermoplastics in that they become chemically crosslinked during final molding and curing. For most practical purposes, they can no longer be melted, reshaped or dissolved. Thermosetting resins are produced in large volume and are extensively used in the construction, housing, and large applicance industries where they may contribute significantly to the fire load in any particular area or product. For this reason, their fire safety characteristics are important. Because of their crosslinked nature, thermosets generally do no soften or drip when exposed to a flame, as do many thermoplastic materials. Their flammability is a function of the thermal stability of the primary chemical bonds and the ease with which volatile gaseous products can be produced by pyrolytic processes to provide fuel for a self-sustaining fire. Many thermosets (e.g. the phenolic resins) provide very little flammable fuel when heated by an ignition source. They produce an insulating char that can only be oxidized at extremely high temperatures and/or high oxygen concentrations. Burning of such materials can be a slow process under many conditions, since the polymer substrate is protected by the surface char. Such resins are inherently fire-retardant and will pass many common laboratory tests without the need for a fire-retardant modification or additive. Their fire retardance is, however, a function of the mechancial ability of the insulating char and is limited by the resistance of elemental carbon to oxidation. Other thermosets (e.g. styrenated polyester resins) do not form chars and burn readily.